[Python-ideas] PEP 505: None-aware operators

[Stephan Houben]

Op di 31 jul. 2018 20:49 schreef Jonathan Fine <jfine2358 at gmail.com>:

> David Mertz wrote:
>
> > `spam?.eggs?.cheese?.aardvark` is NOT redundant for
> > `spam?.eggs.cheese.aardvark`.  The two expressions simply do different
> > things [...]
>
> I agree, assuming ?. is a binary operator.


It isn't.


Given this, in Python (+
> PEP 505) one can write
>
>     tmp = spam ?. eggs
>     val1 = tmp ?. cheese ?. aardvark    # For spam?.eggs?.cheese?.aardvark
>     val2 = tmp . cheese . aardvark    # For spam?.eggs.cheese.aardvark
>

Nope, the introduction of the tmp variable changed the semantics. It isn't
a "chain" anymore so it breaks shortcutting.

To be honest I didn't get this either until it was pointed out to me

>
> No special knowledge of PEP 505 is needed. If val1 is always equal to
> val2, then the dot and None-dot operators must be the same. From the
> assumptions, this is something that can be mathematically proved.
>

And false.


> By the way, there's a widely used programming language in which
>     val = a.method()
> and
>     tmp = a.method
>     val = tmp()
> are not always equivalent. Can you guess which language it is?


Javascript.
I suppose in the same way as x+2 and x*2 are " not always" equivalent.

Stephan



> The answer is in:
>
> https://www.slideshare.net/jonathanfine/javascript-the-easiest-quiz-in-the-world-ever
> (question 6: Dot binds).
>
> I'll now go back to following the example of Steve Bower and Raymond
> Hettinger, which in my words is to wait until we have proper cover for
> the BDFL's vacation.
>
> --
> Jonathan
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